[web] Introduce LoginFormWrapper component

Summary:
Basically wrap LoginForm with RainbowKitProvider and WagmiConfig.

Inspired heavily by (read: copied from) landing/siwe.react.js.

Test Plan: Tested implicitly by subsequent diffs.

Reviewers: ashoat, tomek

Reviewed By: ashoat

Differential Revision: https://phab.comm.dev/D6217